1. Field of the Invention
This invention relates to position measuring transducers, and, more particularly, to a transducer for measuring deflection of an equalizing beam employed in an equalizing beam suspension system.
2. Description of the Prior Art
Weight regulations limiting the load weights of commercial vehicles are almost universally in effect. These regulations generally specify the maximum load of each vehicle axle as well as the maximum total load. Fines are usually levied against operators who are found violating these regulations.
To maximize profits, vehicle operators normally load their vehicles as close as possible to the legal load limit. In order to do this, the vehicle operator must be able to accurately measure the vehicle's weight while the vehicle is being loaded.
Although measuring devices external to the vehicle such as platform scales have long been used for this purpose, recently developed on-board weighing systems have proved their usefulness over such external measuring devices. In some of these systems, strain gauges are generally secured to structural members of the vehicle, usually the axles. In other systems load cells are placed on structural members intermediate the axles and the load such as on the structural member supporting the vehicle bed. Other on-board load measuring systems measure the relative displacement of the springs or the relative displacement between the vehicle frame and axle.
Many problems associated with the above-mentioned on-board vehicle weighing systems have been solved to some extent by a recently developed system described in U.S. Pat. No. 4,042,049. This patent describes an on-board load measuring system which measures the deflection of a pair of transversely spaced, center-mount equalizing beams which are in turn supported at opposite ends by a pair of tandem axles. The transducer for measuring load-induced deflections of the equalizing beams is formed by a strain gauge instrumented measuring beam extending between a pair of mounting pads. The load cell is installed by boring accurately located mounting holes into the equalizing beam, tapping the bores with threads and then bolting the mounting blocks onto the equalizing beam utilizing the threaded bores. Although this system represents a vast improvement over conventional on-board vehicle weighing systems, some problems with the load cell mounting structure have nevertheless arisen. One of these problems is the difficulty in accurately spacing the holes apart from each other so that their position corresponds to the position of mounting bores in the respective mounting blocks. Any deviation from this exact placement prestresses the measuring beam thereby producing an offset in the output of the load cell. Another problem with the mounting structure is that the relatively large force required to bend the measurement beam necessitates that the measurement beam be bolted to the equalizing beam. However, by tapping into the equalizing beam, the distributors of such measuring systems potentially subject themselves to product liability claims in the event of equalizing beam failure. Although there has been no evidence that tapping into an equalizing beam in this manner reduces the strength of the equalizing beam the possibility nevertheless may give rise to unsubstantiated product liability claims.